This invention relates to a variable-crown roll for use in multi-roll rolling mill.
In the rolling of plates, it is important that the plate profile (the thickness distribution in the widthwise direction) be rectangular, that the plate thickness be always constant, and it is particularly important that good shape control be carried out, i.e., that the flatness of the rolled plate be constant. Various new types of rolling mills have been developed in order to meet these requirements. In order to improve the flatness and profile of a plate, it is necessary to compensate the deflection of the work roll, and for this purpose, the work roll bending method, the back-up roll bending method, the double chock bending method, the roll skew method, the roll shift method, the variable-crown roll method (sometimes referred to as the VC roll method), and the like have been developed.
Of these methods, the variable-crown roll method is particularly economical because a conventional rolling mill can be adapted so as to perform variable-crown rolling merely by replacing a conventional roll of the rolling mill with a variable-crown roll. Variable-crown rolls have been effectively employed in combination with existing roll benders for improving the flatness and profile of rolled plates.
In a conventional variable-crown roll, a sleeve is mounted on an arbor by shrink fitting. High-pressure oil is introduced into a pressure chamber at the center of the roll, and the sleeve is made to expand. The limit to the stress which can be applied to the sleeve restricts the amount of roll crown which can be produced to a relatively small value. For example, with a large-sized variable-crown with a diameter on the order of 1500 mm, the maximum amount of expansion which can be achieved is roughly 0.2-0.4 mm/radius. This amount of roll crown is adequate for normal rolling of soft thin sheets. However, when rolling thick plates, even if a conventional variable-crown roll is combined with a bender, the amount of crown which is obtainable is inadequate. In particular, in a roughing mill for hot rolling of aluminum or steel or a rolling mill for thick steel plates, roll crown on the order of 2-3 times the above-described amount is required. Furthermore, even when rolling sheets, if the material being rolled is a hard material or an alloy steel which has a high resistance to deformation, the amount of roll crown obtained with a conventional variable-crown roll can be inadequate.
Some of the above-described rolling methods allow a large amount of control, but they have problems such as that equipment costs are high and that modification of conventional equipment so as to perform these methods takes much time. Accordingly, there has been a desire for the development of a new kind of roll which, like a variable-crown roll, can merely replace a conventional roll, and which provides high performance, is simple, and is also economical.
Multi-roll mills including Sendzimir rolling mills employ eccentric rolls to obtain roll crown. These rolls, however, have not been utilized as a back-up roll or work roll for rolling mills such as 4-high rolling mills, 6-high rolling mills, and 2-high rolling mills.
In addition, the above-described multi-roll mills are for the purpose of shape control during cold rolling, and they have not been utilized for performing profile control during hot rolling.
For example, in a Sendzimir rolling machine, an outermost back-up roll of which is shown in cross section in FIG. 11, a plurality of eccentric rings 3 arranged in the longitudinal direction are mounted on an outermost back-up roll 2 (As-U-Roll) which supports an unillustrated, small-diameter work roll. The roll crown in the longitudinal direction of the roll is adjusted by adjusting the rotational angle of each eccentric ring.
In a differential roll speed rolling mill, a bridle roll of which is shown in cross section in FIG. 12, as indicated by reference FIG. 4, is used as eccentric rolls for performing tension control. The envelope of crown 6 is changed from concave to convex by changing the rotational angle of a shaft 5, whereby the distribution of tensile force applied to a strip is varied (Japanese Laid-Open Specification No. 61-276704(1986)).
Japanese Laid-Open Patent Application Specification No. 61-7003 (1986) discloses a mechanism in which a thin sleeve covers a roll which is divided into a plurality of ring-like sections, each of which is mounted on an arbor and is eccentric with respect to the axis of the arbor. The degree of eccentricity of the sections gradually increases towards the lengthwise center of the arbor. Roll crown can be varied by adjusting the position of each of the divided sections of the roll.
However, with that mechanism, stepped portions are inevitably formed each in the divided roll sections, so when the roll is used as a back-up roll for a work roll, some portions of the back-up roll always remain not in contact with the work roll. As a result, stress concentrates in the corners of the outer periphery of the sleeve of the back-up roll, and the corners of the sleeve can easily form scratches in the sleeve and the work roll. Even if the corner of each of the divided roll sections is made round, this problem is only slightly mitigated and can not be completely solved. It is possible to reduce the size of the stepped portions in the divided roll sections by dividing the roll into a larger number of sections, resulting in a smaller step between each section of the roll. However, doing so increases the complexity of the structure of the roll and makes maintenance more difficult.